1. Technical Field
The present disclosure relates to microchip heaters for microfluidic and micromechanical applications, and more particularly, to a multi layered heating element structure.
2. Description of the Related Art
Some fluids are processed at temperatures that need to be accurately regulated.
DNA amplification process (PCR, i.e., Polymerase Chain Reaction process) is one process in which accurate temperature control, including repeated specific thermal cycles, needs to be carried out, while avoiding thermal gradients in the fluid. Often, only very small amounts of fluid are used, either because of a small sample or the expense of the fluid. Microchip heaters are particularly suited for this application.
Other examples of fluid processing needing specific thermal characteristics include the implementation of chemical and/or pharmacological analyses, and biological examinations. Other situations that require an accurate, miniaturized heater include inkjet printers heaters and optical switching heaters, to name a few.
Current inkjet technology relies on placing a small amount of ink within an ink chamber, rapidly heating the ink and ejecting it to provide an ink drop at a selected location on an adjacent surface, such as a sheet of paper. Traditionally, ohmic resistors which heat up rapidly when current is passed therethrough have been used to provide the necessary temperature increase of the ink. See, for example, a detailed discussion of ink ejection in an article titled “Thermodynamics and Hydrodynamics of Thermal Ink Jets,” by Allen et al., Hewlett-Packard Journal, May 1985, pp. 20-27, incorporated herein by reference.
Generally, present techniques for generating local heating in a microchip include heating elements that are positioned along one side of the object to be heated. The ink is required to be ejected from the reservoir toward its target, which requires raising the temperature of the heater high enough to eject the ink and maintain the ink in a heated state as it exits the microchip. The chamber must then cool rapidly so that new fluid can be inserted into the chamber at liquid temperatures. Since resistor temperatures may reach approximately 800 degrees Celsius, such devices often employ a thick metallic film at the edge of the chamber to serve as a heat sink for preventing high temperatures from adversely affecting the durability of the inkjet cartridge or printer components. The heat sinks are typically fabricated from valuable metals, such as gold. In some designs at least one gram of gold is used for each wafer of the semiconductor material. Accordingly, manufacturing large quantities of such devices requires large quantities of gold, significantly adding to the cost of manufacturing and the retail price of such devices.